Many years ago before we had a smallholding we once grew tomatoes which were very much taller than yours Phil by the time it came round to planting out time. So we took them down to our allotment and dug a long trench, filled with lovely manure etc. We laid the tomatoes down along the trench so just a couple of pairs of true leaves were above ground. They rapidly grew a huge root system along the whole of the buried stems, and eventually made some very sturdy plants, with a very heavy crop.